1. Field of the Invention
This invention relates to a method for the treatment of potassium bisulfate to prevent caking of the dried solid material and to the novel compositions produced by treatment of the bisulfate with phosphate rock.
2. Description of the Prior Art
Potassium bisulfate is a compound of the formula KHSO.sub.4 and is known in the art as being useful in various areas including use as an intermediate in the production of certain fertilizers. For example, this compound is disclosed in U.S. Pat. Nos. 3,718,453 and 3,697,246 as a valuable intermediate in the production of fertilizers.
In operation of commercial plants in which potassium bisulfate is used, large quantities of solid potassium bisulfate are necessarily shipped and stored prior to actual use. Potassium bisulfate however, is hygroscopic and therefore has a tendency to cake during storage and shipment which makes it difficult to transfer and use. Accordingly, consideration has been given to developing procedures and methods by which the caking tendency of potassium bisulfate can be prevented in an economic manner without deleteriously affecting the potassium bisulfate. According to the present invention, it has been found that the addition of phosphate rock to solid potassium bisulfate unexpectedly inhibits caking tendencies of potassium bisulfate. This is unexpected in view of the acid nature of potassium bisulfate.
Phosphate rock is a natural product which is a mixture of materials and is considered to have the following formula: EQU Ca.sub.9 (PO.sub.4).sub.6.CaF.sub.2
and generally comprises calcium phosphates with some fluorides admixed therewith probably in the form of calcium fluoride. This product has also been used in the art to prevent caking of fertilizers including ammonium and potassium salts, calcium nitrates, and the like. The use of phosphate rock as an anti-caking agent of this type is disclosed in U.S. Pat. Nos. 2,008,469 and 2,307,253. In addition, U.S. Pat. No. 3,419,379 discloses use of phosphate rock in a two step treatment for providing coatings on fertilizers such as calcium phosphate although potassium sulfate (K.sub.2 SO.sub.4) is also mentioned as a plant nutrient.
The present invention, however, is considered to distinguish from these patents and is concerned with a novel composition of matter and an unexpectedly simple procedure for inhibiting the caking tendency of potassium bisulfate by use of phosphate rock.